The present invention relates to a circuit breaker such as an auto-breaker for protecting low-voltage distribution equipment from an over-current, and more specifically, a circuit breaker having an auxiliary switch for detecting ON/OFF states of a main circuit contact as an electric signal.
As an example of a circuit breaker, a structure of a conventional auto-breaker with an auxiliary switch attached to a main body housing is shown in FIGS. 7 and 8(a)-8(c). In FIG. 7, reference numeral 1 denotes a main body housing (molded resin housing) of the circuit breaker; reference numeral 2 denotes a current breaking section of a main circuit incorporated in the main body housing 1; reference numeral 3 denotes a switching mechanism section; reference numeral 4 denotes an over-current tripping device; reference numeral 5 denotes an operating handle for switching; reference numeral 6 denotes a switching lever of the switching mechanism section 3 for opening and closing a contact of the main circuit in the current breaking section 2; and reference numeral 7 denotes a cassette type auxiliary switch (an auxiliary switch that detects ON/OFF states of the main circuit contact as an electric signal) as an auxiliary (optional) equipment inserted into and detachably attached to a pocket-shaped auxiliary equipment storage section 8 formed on an upper surface of the main body housing 1.
The switching mechanism section 3 is comprised of a toggle link mechanism that moves in response to on/off operations of the operating handle 5 or an output of the overload current tripping device 4, and the switching lever 6 that opens or closes the main circuit contact in response to a movement of the toggle link mechanism. As shown in FIG. 7, the switching lever 6 is a seesaw-type lever that swings around a pivot 6b. An operational end 6a of the switching lever 6 faces a top of a contact holder 2b supporting a movable contact 2a of the current breaking section 2.
In response to the turning-off operation, a drive spring (not shown) is released to drive the switching lever 6 clockwise to push the movable contact holder 2b to open the main circuit contact. Conversely, in response to the turning-on operation, the switching lever 6 swings counterclockwise back to a position above the movable contact holder 2b while the drive spring is restored, thereby closing the main circuit contact. A leading end 6c of the switching lever 6 projects toward the auxiliary equipment storage section 8 to function as an actuator for turning on/off the auxiliary switch 7 attached to the auxiliary equipment storage section 8.
With the above arrangement, when the operating handle 5 is manually operated to the ON or OFF position, the main circuit contact in the current breaking section 2 is opened or closed through the switching lever 6 in the switching mechanism section 3. When an over-current flows through the main circuit, the over-current tripping device 4 sends an output signal to trip the switching mechanism 3 to open the main circuit contact as described above.
As shown in FIGS. 8(a)-8(c), the auxiliary switch 7 is comprised of a housing (molded resin) 7a. In the housing 7a, there are disposed fixed contacts 7b, bridging movable contacts 7c, a movable contact holder (a slider capable of moving up and down) 7d, a return spring 7e for the movable contact 7c, and an operating lever 7f connected to the movable contact holder 7d. A molded resin cover 7g covers a front of the housing 7a so that the auxiliary switch 7 is configured as a cassette type limit switch.
When the cassette-type auxiliary switch 7 is inserted into and attached to a predetermined position of the auxiliary equipment storage section 8 in the main body of the circuit breaker, the operating lever 7f overlaps the leading end 6c of the switching lever 6 in the main body of the circuit breaker, so that the auxiliary switch 7 is connected to the switching mechanism section 3 in the main body of the circuit breaker.
The auxiliary switch 7 operates as follows. In the ON state of the circuit breaker in which the main circuit contact is closed, the leading end 6c of the switching lever 6 is located at a lowered position. As a result, the return spring 7e pushes down the movable contact holder 7d of the auxiliary switch 7, so that the movable contacts 7c are released from the fixed contacts 7b (turning off the switch contact). According to the switch signal, it is detected that the main circuit contact is turned on.
On the other hand, in the OFF state of the circuit breaker in which the main circuit contact is opened by the operation of the handle or the tripping operation of the tripping device, the leading end 6c of the switching lever 6 swings clockwise to push up the operating lever 7f of the auxiliary switch 7 against the return spring 7e. As a result, the movable contact 7c and the fixed contact 7b are closed, and the auxiliary switch 7 sends the switch signal of turning off.
In the conventional structure shown in FIGS. 8(a)-8(c), a wedge locking claw 7h projecting from a lower part of the front surface of the cover 7g of the switch housing 7a is provided, so that the auxiliary switch 7 inserted in the auxiliary equipment storage section 8 in the main body of the circuit breaker is locked at a predetermined position. When the auxiliary switch 7 is pushed into the auxiliary equipment storage section 8 of the main body housing 1 as shown in FIG. 7, the claw 7h is hooked by snap-fitting on an engagement projection 8a formed on an inner wall surface of the auxiliary equipment storage section 8 to lock the auxiliary switch 7 at the predetermined position.
The conventional structure shown in FIGS. 7 and 8(a)-8(c) has the following problems in terms of the structure for supporting the auxiliary switch 7.
When the auxiliary switch 7 is inserted and pushed into the auxiliary equipment storage section 8 of the main body housing 1, the engagement claw 7h provided on the housing cover 7g of the auxiliary switch 7 hooks on the engagement projection 8a of the auxiliary equipment storage section 8. In this process, the housing cover 7g itself needs to be flexible so that the engagement claw 7h can move over the engagement projection 8a. However, if the cover 7g is flexible, when an external force is applied to the cover 7g, the cover deforms to change a posture of the auxiliary switch 7. Accordingly, the auxiliary switch 7 connected to the switching lever 6 in the main body of the circuit breaker becomes unstable to operate.
Further, with the configuration described above, it is difficult to release the engagement claw 7h from the engagement projection 8a when the auxiliary switch 7 is pulled out of the main body of the circuit breaker. In addition, when the auxiliary switch 7 is attached to and detached from the main body repeatedly, the locking part is deformed and worn down, thereby making it difficult to position the auxiliary switch 7 steadily and deteriorating the reliability.
In addition to the locking method using the snap-fitting as described above, Japanese Patent Publication (Tokkai) No. 07-169355 has disclosed a latch mechanism incorporated into an auxiliary switch. The latch mechanism is hooked on an auxiliary equipment storage section in the main body of a circuit breaker to lock the auxiliary switch at a predetermined position. However, with this mechanism, a structure of the auxiliary switch tends to be complicated and increase an outside dimension of the auxiliary switch, thereby deteriorating the space efficiency.
It is therefore an object of the present invention to provide a circuit breaker having an improved mounting structure of an auxiliary switch with a simple arrangement so that the auxiliary switch can be steadily locked at a predetermined position when the auxiliary switch is attached to the main body of the circuit breaker.
Further objects and advantages of the invention will be apparent from the following description of the invention.